In the concrete industry, when building bridges, buildings, roads and the like, it is often necessary to pour large horizontal slabs of concrete. Once poured, it is usually necessary to machine the slab. Such machining may include cutting seams completely through the slab (to form expansion joints and to allow for foundation shifting), cutting notches partially into the slab (to create stress cracks along which the slab will split), cutting multiple grooves into the slab to create a high friction surface such as for bridges, grinding the surface of the slab and the like. Various types of concrete saws may be utilized to carry out these machining tasks. In larger industrial applications, large self-propelled saws are used which are powered in a variety of manners, such as by gasoline, diesel, electric, propane and natural gas engines mounted on the saw. While performing a cut, the operator walks behind the saw to control the direction, cutting speed, cutting depth and the like.
Typical self-propelled concrete saws are mounted upon rear drive wheels and upon a hinged front axle assembly which raises and lowers the front end of the saw. The front axle assembly includes a height adjustment cylinder that is attached to a front axle assembly having the front wheels thereon. The front axle assembly pivots downward away from, and upward toward, the saw frame when the cylinder extends and retracts thereby raising and lowering the saw. The saw blade is mounted upon a blade support shaft proximate the front of the saw and thus as the front end is raised and lowered, the cut depth is varied.
Conventional concrete saws include a gasoline, diesel, propane (internal combustion), hydraulic and air or electric engine aligned along an axis transverse to the longitudinal axis of the saw frame. This transverse arrangement aligns the engine crankshaft parallel to the rotational axis of the saw blade, to afford an easy design for interconnecting pulleys upon the crankshaft and the saw blade.
Conventional internal combustion (nonelectric) powered concrete saws utilize a mechanical governor for controlling the RPMS (revolutions per minute) of the engine and the saw blade. Every type of saw blade operates at a different optimal rotational speed. The optimal speed for a given blade is maintained by using a specific pulley size to blade size ratio. This requires changing the pulleys in the drive system to accommodate specific blade sizes. If optimal speed is not maintained, engine power is lost and blades can be damaged. Most nonelectric powered concrete saws are designed to operate with a plurality of blade sizes and they are capable of rotating at extremely high speeds.
Most prior art internal combustion saws only operate at one cutting blade speed. Because different saw blades operate at peak performance at different rotational speeds, saw performance is limited due to a single speed drive system. Thus, there is a need to vary blade speed based on the particular blade being used or the sawing conditions encountered. The prior art provides multispeed drive systems for concrete saws. However, such saws rely on complex, costly and/or limited service life transmissions or hydraulic drive systems. Some hydraulic systems require water cooling that prevents use of the saw for dry cutting operations. Also, in some prior art multispeed machines, the pulleys are so large that they interfere with a saws ability to make a cut of acceptable depth. Thus, the need exists for an internal combustion powered concrete saw capable of operating at different rotational cutting speeds having a dependable and simple multispeed drive system.